Trend and Variability of Pineapple Express Events Depicted by
Six Reanalysis Datasets
Martin Schroeder, S.Y. Simon Wang, and Robert Gillies.
[email protected]
Utah Climate Center – Dept. of Plants, Soils, and Climate. Utah State University, Logan, UT
Atmospheric River
(Non - Pineapple
Express)
Reanalysis Datasets Used
NCEP/NCAR Reanalysis I
2. NCEP/DOE Reanalysis II
3. NOAA-CIRES 20th Century Reanalysis V2 (20CR)
4. ECMWF Interim Reanalysis (ERA-Interim)
5. NASA Modern Era Reanalysis for Research and Applications (MERRA)
6. NCEP Climate Forecast System Reanalysis (CFSR)
7. US/Mexico Precip (1°x1°) Climate Prediction Center (NOAA)
1.
Not of primary
interest to this study
Generally does not
sustain a consistent
pattern
Pineapple Express
Event.
Methods
To determine the conditions leading to P.E. events, we first created a composite
representing 12 “classic days” from 4 storms corresponding to literature coverage.
We then created an index to define PE events by considering:
1)The southerly and westerly components of column integrated water vapor flux (Q)
at 2 locations downstream of the region of interest. 2) 850 mb geopotential height (Z)
in the subtropical region off the west coast of Mexico. 3) The spatial correlation of |Q|
fields relative to the ‘classic case’ composites.
Requisite conditions:
( Z-mean>0) , (Uq>75, Vq>50), (Uq>75, Vq>0)
(upstream)
(downstream)
(scorr|Uq|>0.85)
FOR 2 OR MORE CONSECUTIVE DAYS
• Precipitation was excluded as a variable in the index.
• From this definition, a list of dates meeting the criteria were isolated and analyzed
using 6 reanalysis datasets.
New Year’s 1997
storm
Peak flood in many
Northern California
Rivers
Type of event isolated
by this study
Northern California High-Impact Cases:
11–24 February, 1986 (Leung and Qian 2009)
29 December, 1996 – 4 January,1997 (Galewsky, J., A. Sobel,
2005)
16–18 February, 2004 (Ralph, F. M., P. J. Neiman, G. A. Wick, S. I. Gutman, M.
D. Dettinger, D. R. Cayan, and A. B. White, 2006)
29 December, 2005 – 2 January, 2006 (Smith, B.L., S.E. Yuter, P.J.
4 Panel plot showing the frequency and linear trends in the number of Pineapple Express days per year
and the number of Pineapple Express events per year. All days meet criteria set out in PE Index
Neiman, and D.E. Kingsmill, 2010)
Composites of PE events from Six Reanalysis Datasets
Winter U (200mb) 145 ° W
Longitude
Linear Trend
Linear Trend
Linear Trend
Linear Trend
All events resulted in
significant flooding of Northern
California Rivers
3 days representing ‘classic’
Pineapple Express conditions
were taken from each storm
and used to create composites
Observations:
Over 31 years:
Decline in total winter
precipitation over
northern California was
observed.
(mm)
Trend in Total Precip
Trends in Residual P not from PE Conditions
•
Linear Trend
Linear Trend
(0.1
mm/
day)
Vectors show magnitude and direction of water vapor flux (Q) (kg*m*s-1*kg-1) from
selected high impact days.
Contours show streamfunction or rotation/circulation of water vapor flux (Q) (m2*s-1*kg-1)
Analysis of winter (Nov-Mar) 200mb U
winds reveals a northward shift and
weakening in the mid-latitude jet,
coinciding with a decrease in winter
precipitation over northern California
during the same time period.
A decreasing trend in
Pineapple Express
storms impacting
northern California was
observed.
Decline in percent
contribution to total
winter precipitation from
PE storms similarly
observed.
•
•
•
Trend in Total Precip
•
SUMMARY AND FUTURE
ANALYSIS
Decline in Northern California
Precipitation coincides with reducing PE
events
Is the frequency of these events declining,
or is a spatial shift occurring (influence of
shifting/weakening 200mb U jet)?
What other mechanisms caused the
residual precipitation? (further analysis)
Expand study to other regions (i.e. Pacific
Northwest/ So. California)